Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
  • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
  • G01N33/53—Immunoassay; Biospecific binding assay; Materials therefor
  • G01N33/569—Immunoassay; Biospecific binding assay; Materials therefor for microorganisms, e.g. protozoa, bacteria, viruses
  • G01N33/56983—Viruses
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2333/00—Assays involving biological materials from specific organisms or of a specific nature
  • G01N2333/005—Assays involving biological materials from specific organisms or of a specific nature from viruses
  • G01N2333/08—RNA viruses
  • G01N2333/18—Togaviridae; Flaviviridae
  • G01N2333/183—Flaviviridae, e.g. pestivirus, mucosal disease virus, bovine viral diarrhoea virus, classical swine fever virus (hog cholera virus) or border disease virus

Definitions

• the invention pertains to the field of immunoassay tests for viral infection. More particularly, the invention pertains to the development of an antigen-capture immunoassay that can use serum, plasma, milk, mucosal fluid, or urine samples to identify animals infected with the bovine viral diarrhea virus.
• Bovine viral diarrhea virus currently represents a major threat to the cattle industry. First described over fifty years ago, this pathogen has been found to be both highly virulent and easily spread. Considered a primary pathogen of the bovine enteric, respiratory, reproductive, and immune systems, BVDV continues to cause significant economic losses to the cattle industry worldwide. Recent outbreaks have occurred in Canada, the US, and throughout the world. To help combat these problems, a simpler, more cost effective method of BVDV detection, capable of yielding results in a timely fashion, is needed to better control the spread of the BVDV virus within the cattle population. Such a diagnostic tool is particularly important in light of the ineffectiveness of currently available BVDV vaccines.
• BVDV Classified as a member of the genus Pestivirus and Flaviviridae family, BVDV is closely related to sheep border disease virus (BDV), and hog cholera virus (HCV), both of which are serologically related pestiviruses. Entire or partial genomic sequencing of pestivirus isolates has allowed the determination that a high degree of sequence conservation is present among the pestiviruses. More recently, antigenic variants of BVDV have been identified, and BVDV strains have been divided into two distinct genotypes, type 1 and type 2, which have been further subdivided, based upon cytopathogenicity.
• BDV sheep border disease virus
• HCV hog cholera virus
• BVDV Molecular cloning, and Polymerase Chain Reaction (PCR) technology have determined that the general structure of BVDV consists of a capsid protein and three envelope glycoproteins.
• the genome of BVDV is a 12.3 kb RNA consisting of a single open reading frame (ORF).
• ORF open reading frame
• the BVD virus is itself a small, enveloped RNA virus with positive strand polarity. This positive strand aspect of the viral genome allows the RNA to be infectious, even in the absence of virion proteins.
• the BVDV is spread through the herd in a fecal-oral manner, attacking the enteric, respiratory, reproductive, and immune systems.
• the viral load needed to provoke symptomatic infection is correlated with the type and strain of BVD virus.
• BVDV has the ability to infect fetuses by crossing the placenta, often resulting in a spontaneous abortion of the fetus, and a resultant decreased fertility among infected animals.
• Strategies for control of BVDV range from stricter management practices, in an effort to simply reduce economic loss, to elaborate testing procedures to identify infected animals that, while effective, would entail an unacceptable level of cost. Failure of field vaccinations for BVDV have increased the need for a test protocol that will help identify and eliminate infected animals in a cost-effective way.
• BVDV like other infectious disease agents, is associated with a wide variety of clinical manifestations, creating a very difficult diagnostic challenge. Common manifestations of BVDV infection can include: abortion storms, infertility, irregular heat cycles, early embryonic deaths, fetal mummification, immuno-suppression, dysentery, thrombocytopenia, and cerebral hypoplasia. Moreover, serological studies have shown that a high percentage of cattle infected with BVDV, including those considered to be persistently infected (PI), remain clinically asymptomatic. Such conditions make it imperative that a reliable, inexpensive, and easy to use test be developed to assist in the detection of BVDV-infected animals in cattle herds.
• PI persistently infected
• the BVD virus is typically maintained in a herd due to the presence of immunotolerant persistently infected carrier animals. These PI cattle are exposed to the virus in utero , but can remain clinically asymptomatic throughout the course of their lives, continually shedding fecal matter, and bodily fluids, with a high concentration of virus, and thereby posing the threat of infection for other animals as long as they remain in the herd.
• the virus may be present in more than half of the cattle in a herd before signs of an outbreak exhibit themselves. Symptoms of the disease are usually preceded by leukopenia, and testing efforts to date have focused on identifying this effect.
• BVDV cases increased 23% in less than one year.
• species it was first found to be associated with e.g. cattle
• pestiviruses can cross species barriers. This indicates that in areas in which wild, free-ranging ruminants (moose, buffalo, etc.) are exposed to infected cattle herds, these animals are also susceptible to infection from BVDV, or can alternatively act as a reservoir of virus capable of infecting a previously "clean" herd.
• EO epitope of the BVDV gp48
• the mAb 15.c.5 is currently available through the Diagnostic Laboratory at the College of Veterinary Medicine, Comell University, Ithaca New York.
• ELISA test has been developed which utilizes a monoclonal antibody (mAb), specific for BVDV viral proteins or protein fragments, to recognize their presence in bovine serum, plasma, milk, urine, or mucosal fluid.
• mAb monoclonal antibody
• the important aspect of this ELISA test is that this ELISA provides for the detection of the target viral proteins in serum, milk, plasma or other bodily fluid. Typically white blood cells must be collected and extracted, requiring a time consuming and labor intensive sample preparation procedure.
• mAb 15.c.5 which allows the development of an assay for BVDV from sera, plasma, milk, urine or mucosal fluid, Applicants found that they were able to construct a distinctly improved immunoassay test kit.
• the immunoassay provided thereby is accurate, has a shorter turn around time for a given test sample, and is an economically much more feasible option for those in the cattle industry.
• the target epitope of this mAb is located on gp48, also known as "E ms " and "E0".
• Applicants have optimized their ELISA test such that it has enhanced reliability, and reveals excellent agreement when compared with the conventional, and most sensitive, method of BVDV detection -- viral isolation.
• Applicants have developed their bovine ELISA into an easy to use, reliable, quick, and cost effective kit that will aid veterinarians in their efforts to identify BVDV infected animals, especially those PI animals, and remove them from a given herd. This in turn protects the cattle industry from significant economic loss due to BVDV. Since BVDV can affect other ruminants this assay can be used on wild animal populations (e.g. deer, moose, elk) to determine if they are BVDV positive. This use could aid in the management of wild animal populations and assist in the removal of reservoirs of BVDV virus outside the domestic cattle population.
• wild animal populations e.g. deer, moose, elk
• BVDV Bovine Virus Diarrhea
• BVDV maintains itself in the bovine population through persistently infected (PI) animals.
• PI persistently infected
• This type of animal results from fetal infection with the BVD virus. If the fetus survives to term, the resulting calf will be incapable of mounting an immune response against the virus and will be persistently infected with the virus for the rest of its life.
• a PI animal may live for years; during this time it will excrete a large quantity of virus into the environment and remain potentially infective to other animals.
• the BVDV serum immunoassay can be either a sandwich type immunoassay, employing the GP-48 specific antibody (as capture or detector antibody) and another anti-BVDV antibody (as a detector or capture antibody to complement the GP-48 specific monoclonal), or a competitive type immunoassay, employing the GP-48 specific monoclonal antibody with a labeled GP-48 antigen or GP-48 antigen attached to a solid phase.
• the capture antibody for example, can be attached to a variety of different solid phases to enable the washing away of unreacted assay reagents during the course of the assay. These include: microwells, coated test tubes, coated magnetic particles, wands or sticks, and membranes (nitrocellulose and others).
• the capture antibody also referred to as primary antibody
• a secondary binder such as protein A, protein G, a secondary antibody specific for the primary antibody, avidin, or an antibody specific for a particular ligand (i.e.: biotin, dinitrophenol, fluorescein, and others)-
• ligand i.e.: biotin, dinitrophenol, fluorescein, and others
• the GP-48 antigen can be attached to a solid phase by passive adsorption, covalent coupling, or by using a solid phase pre-coated with a secondary binder such as avidin or an antibody specific for a particular ligand such as dinitrophenol, fluorescein and others.
• a secondary binder such as avidin or an antibody specific for a particular ligand such as dinitrophenol, fluorescein and others.
• avidin or any of the ligand specific antibodies it is necessary to covalently attach the ligand to the GP-48 antigen.
• a variety of labels can be employed in sandwich or competitive type immunoassays.
• the possibilities include: an enzyme such as peroxidase or alkaline phosphatase, a fluorophore such as fluorescein, a chemiluminescent probe such as an acridinium ester, a time-resolved fluorescent probe such as a europium chelate, a radioactive species, or particles such as colloidal gold, plain latex, or dyed latex.
• the GP-48 specific monoclonal antibody or the anti-BVDV antibody can be either directly labeled by covalent coupling or a labeled secondary antibody that is specific for the corresponding primary antibody and can be used without the need to chemically modify the primary antibody.
• a labeled secondary binder such as avidin or a labeled antibody specific for a particular ligand (i.e.: dinitrophenol, fluorescein, and others) can also be employed. In the case of avidin or any of the ligand specific antibodies, it is necessary to covalently attach the corresponding ligand to the primary antibody.
• the GP-48 antigen can be labeled directly by covalent coupling or a labeled secondary binder such as avidin or a labeled antibody specific for a particular ligand (i.e.: dinitrophenol, fluorescein, and others) can be employed.
• a labeled secondary binder such as avidin or a labeled antibody specific for a particular ligand (i.e.: dinitrophenol, fluorescein, and others) can be employed.
• avidin or any of the ligand specific antibodies it is necessary to covalently attach the corresponding ligand to the GP-48 antigen.
• PI persistently infected
• This kit claimed herein is based on the ELISA methodology, and it employs a BVDV antigen specific monoclonal antibody as the capture antibody, with a goat polyclonal anti-BVDV antibody as the detector, and a Horseradish Peroxidase - anti-goat antibody as the conjugate.
• the test results may be determined through the use of a microplate spectrophotometer wherein an optical density is read at 450 nanometers.
• the concentration of detector antibody, the particular anti-goat conjugate and its concentration, the formulation of the reagent diluent buffer, the formulation of the NSB (non-specific binding) reagent; and the type of microwell were all optimized to yield the lowest background and highest signal-to-noise ratio.
• the reagent configuration i.e. 10x concentrates of detector reagent, enzyme conjugate reagent and NSB reagent, with a separate reagent diluent buffer was designed to maximize kit stability and shelf life.
• bovine gamma globulin was a key additive in the reagent diluent buffer (this reagent diluent buffer is used to prepare working solutions of detector antibody and enzyme conjugate); this additive significantly reduced the background signal.
• the second breakthrough involved well coating. It is advantageous to utilize a purified monoclonal antibody rather than a crude ascites preparation for well coating to insure consistency between batches of coated microplates.
• a purified monoclonal antibody rather than a crude ascites preparation for well coating to insure consistency between batches of coated microplates.
• the background signal was found to be unacceptably high. It was discovered that this high background problem could be alleviated by the addition of bovine albumin to the purified 15.c.5 prior to well coating.
• the ELISA procedure is carried out at room temperature, and takes approximately 4 hours to complete, though it does not require highly specialized laboratory facilities.
• the volume of sample (serum, plasma, milk, urine, or mucosal fluid) required for purposes of this assay procedure is at least 100 ⁇ l per well. Only samples from pre-colostral newborn calves or calves older than 3 months of age are suitable for testing in this ELISA kit. Maternal anti-BVDV antibodies, which can be passed to newborn calves in the first 24 hours of colostrum intake, can interfere with this ELISA to produce false negative results in PI calves. Since the level of maternal antibody decreases as the calf ages, this interference can be prevented by specifying age requirements for animals being tested by this ELISA (Palfi et al., 1993).
• each kit will contain one negative control and one positive control. These controls will be included within each run to insure that each run is valid and to be used in the data reduction calculation (to "normalize” the sample results): These controls, as well as all the other reagents used in the assay presented in this application are preserved with the addition of thimerosal.
• the detector reagent, enzyme conjugate reagent, non-specific binding inhibiting reagent (e.g. the "NSB” reagent) and the ELISA wash buffer are supplied as 10X concentrates.
• the Reagent Diluent Buffer, the negative control, the positive control, TMB substrate reagent, and a solution that will stop the reaction are supplied in the kit in a ready-to-use form with no need for dilution.
• the samples are run in one of two 96-well plates provided in the kit.
• BVDV Antigen Test Kit ELISA Other compounds or resources needed to perform the BVDV Antigen Test Kit ELISA include among other things: de-ionized water, a microplate reader capable of making an optical density (OD) reading at 450nm, serological pipets, and precision pipettors.
• OD optical density
• Directions for the preparation of reagents is included within the literature included with the kit, and broadly refers to the proper procedures and use of the reagents provided in the kit.
• the user should employ the needed number of micro wells from one or more of the provided 96-well plates.
• the microwells themselves can be removed from the plates provided, any excess wells should be saved for future assays.
• the wells are first pre-wetted by pipetting 0.2ml of ELISA Wash Buffer into each well; this buffer should then be removed or poured off the wells prior to the addition of sample.
• the working Detector Reagent should then be prepared by mixing 1 part of the Detector Reagent - 10X concentrate, 1 part of NSB Reagent 10X concentrate, and 8 parts of Reagent Diluent Buffer.
• the reagent Diluent Buffer should be prepared within approximately 1 hour of anticipated use.
• the Reagent Diluent Buffer should be prepared within approximately 1 hour of anticipated use. After the incubation period, remove liquid from the wells as described above, and wash the wells a total of three times as described above. Thereafter pipette 0.1 ml of working Enzyme Conjugate Reagent into each microwell. When this is accomplished cover the wells with adhesive film and incubate at room temperature for 1 to 1.5 hours. While this incubation is ongoing retrieve the TMB Substrate Reagent and Stop Solution and allow them to equilibrate at room temperature or remain at room temperature.
• the data is reduced by first calculating the average raw OD (optical density) for each control and sample assayed.
• the average OD value obtained for the Negative Control is then subtracted from each of the other average raw OD values to obtain blank-corrected OD values for the corresponding positive control and samples. This step eliminates the background noise (due to non-specific binding of enzyme conjugate) from the specific signal.
• a "normalized” OD is then calculated for each sample by dividing the blank-corrected OD of that sample by the "blank-corrected" OD of the Positive Control. Normalizing the results in this manner greatly diminishes the run-to-run variation.
• the normalized OD values thus gained are compared with the following guidelines to determine the BVDV status of the animal, see Table 1, below. Optical Density Chart for the Determination of BVDV Status "Normalized” OD Values BVDV Status Less than 0.20 BVDV NEGATIVE 0.20 to 0.39 "Gray Zone" Greater than 0.39
• the sample should be re-assayed using the standard working reagents as previously used and also assayed without detector antibody in the working detector antibody reagent.
• the raw OD obtained without detector should be subtracted from the raw OD obtained with detector; this difference should then be divided by the blanked OD of the positive kit control (the OD of the negative kit control should be used to blank the positive kit control as usual).
• a new normalized value less than 0.2 should be considered BVDV negative, a new normalized OD value of 0.2 or greater should be considered BVDV-positive.
• raw OD values e.g., unblanked
• Raw OD Values Negative Control ⁇ 0.5 Positive Control > 0.8 ELISA results on bovine serum samples using the purified 15.c.5 preparation as capture antibody on the microwells (A total of 129 animals were tested; Viral Isolation Results were used as a correct reference determination.)
• BVDV-negative by virus isolation BVDV-positive by virus isolation Confirmed PI animals The number of samples tested in each category 104 25 7 BVDV Ag Test Kit results for each category of samples Number of test kit negatives 104 0 0 Number of test kit positives 0 25 7
• BVDV-Positive result in the ELISA may not always be indicative of a persistently infected animal.
• a definitive diagnosis that a particular animal is persistently infected should only be made after a second sample is taken from the subject animal at least 3 weeks after the initial sample and that second sample is also found to be BVDV-positive.

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• 1997
  • 1997-09-23 US US08/935,644 patent/US6174667B1/en not_active Expired - Lifetime
• 1998
  • 1998-09-23 WO PCT/US1998/019810 patent/WO1999015900A1/en not_active Ceased
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